1. Technical Field
The invention relates to a method for measuring density, a printing method, a method of calculating a correction value, a method of manufacturing a printing apparatus, and a method for obtaining a correction value.
2. Related Art
There is known a printing apparatus which prints a print image on a medium (such as paper, cloth, and OHP film) by repeating alternately the following actions: a dot formation action in which dots are formed on the medium by ejecting ink from a head moving in a movement direction and a carrying action in which the medium is carried. The print image printed with the printing apparatus is formed by lining up in a carrying direction a myriad of pieces of image which consist of dot rows.
The dot row which each piece of image consists of is formed by making an ink droplet ejected from a nozzle of the head land on the medium. If an ink droplet of ideal size lands on an ideal position, each of the dot rows is formed in their respective predetermined region (row region), and a piece of image with ideal density is formed in the region. However, actually, because of influence by variation in precision of manufacturing and the like, variation in density occurs among the pieces of image formed in the respective regions. As a result thereof, a streaky unevenness in density occurs in the print image.
Therefore, technologies for suppressing this unevenness in density and improving print image quality are proposed (see JP-A-2-54676 and JP-A-6-166247, for example).
An image processing unit disclosed in JP-A-2-54676 performs sampling of an image by a CCD sensor and outputs the digitized data through an inkjet printer. In order to correct unevenness in density, an image processing unit disclosed in JP-A-2-54676 stores as coefficients characteristics of variation in gain of the CCD sensor and characteristics of unevenness in density of a head, and performs binarization in contemplation of these coefficients.
In a method of correcting unevenness in recorded density which is disclosed in JP-A-6-166247, patterns for detecting unevenness in density are printed and unevenness in density is corrected based on density data of the patterns for detecting unevenness in density.
JP-A-2-54676 does not disclose how to obtain coefficients reflecting characteristics of variation in gain of the CCD sensor. Accordingly, depending on a method for obtaining these coefficients, there are cases in which these coefficients cannot reflect characteristics of the CCD sensor properly. If these coefficients do not reflect characteristics of the CCD sensor properly, unevenness in density occurs in a print image. In JP-A-6-166247, after the patterns for detecting unevenness in density are printed, the patterns for detecting unevenness in density are read by an image sensor, and density data is created. However, if an image sensor cannot read the patterns for detecting unevenness in density properly, unevenness in density cannot be corrected properly and unevenness in density occurs in a print image.